1. Field of the Invention
The present invention relates generally to telecommunications systems and more particularly to wireless communication systems and the conversion of an International Mobile Station Identity (IMSI) number from one format to another format to allow global roaming capability within a code division multiple access (CDMA) cellular communications system.
2. Description of the Related Art
CDMA wireless telephones, hereinafter referred to as mobile stations (MS), register with a Mobile Switching Center (MSC) via a base station (BS) by. transmitting an encoded associated identification number known as the International Mobile Station Identity (IMSI) number to the serving BS.
The IMSI number consists of up to fifteen numerical characters (0-9). An IMSI consists of a three digit mobile country code (MCC) and a variable length national mobile station identity (NMSI). The NMSI consists of two variable length parts: the mobile network code (MNC) and the mobile station identification number (MSIN). A Class 0 IMSI is fifteen digits in length. A Class 1 IMSI is less than fifteen digits in length.
In the United States the variable length MNC and MSIN are set by the FCC to three digits and nine digits respectively. This results in IMSI numbers having a length of fifteen digits. A country may set the length of the MNC to be either one, two or three digits and the length of the MSIN to be between one and eleven digits. The length of the MNC plus the length of the MSIN must be no more than twelve digits.
An IMSI number is stored in CDMA wireless telephones as three parameters: MCC, IMSI_11_12, and IMSI_S. These IMSI parameters are transmitted from the mobile station to the base station. Additional information that may be transmitted from the mobile station to the base station along with the IMSI number may include an IMSI length indicator, the IMSI Class and the IMSI Type, as described further below. To ensure compatibility between a mobile station and a base station from different manufacturers, the procedures and protocol for the format and transmission of messages from an MS to a BS have been standardized. For an identification of industry standards relating to CDMA cellular communications systems, reference is made to TIA/EIA Standard IS-95, entitled xe2x80x9cMobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System.xe2x80x9d Accordingly, the IMSI number is transmitted in a format compliant with TIA/EIA/IS-95, and includes the three parameters MCC, IMSI_11_12, and IMSI_S.
FIG. 1 is a block diagram of a conventional mobile network illustrating a mobile station (MS) 14 communicating with a mobile switching center (MSC) 10. System configuration and operation of a code division multiple access (CDMA) cellular communications system is well known to those skilled in the art. Accordingly, detailed information concerning CDMA system configuration and operation is not provided. However, technical information concerning this topic may be obtained by referring to a number of available documents. For example, for a description of the use of CDMA techniques in a multiple access communications system, reference is made to U.S. Pat. No. 4,901,307, entitled xe2x80x9cSpread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters.xe2x80x9d Furthermore, for a description of the generation of signal waveforms for use in a CDMA communications system, reference is made to U.S. Pat. No. 5,103,459, entitled xe2x80x9cSystem and Method for Generating Signal Waveforms in a CDMA Cellular Systemxe2x80x9d and U.S. Pat. No. 5,883,888, entitled xe2x80x9cSeamless Soft Handoff in a CDMA Cellular Communications System.xe2x80x9d The disclosures of the foregoing references are expressly incorporated by reference herein.
The heart of a typical wireless telecommunications system is the Mobile Switching Center that is connected to a plurality of base stations that are dispersed throughout the geographic area serviced by the system. The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially distinct areas called xe2x80x9ccells.xe2x80x9d Each MSC is responsible for, among other things, establishing and maintaining calls between mobile stations and between a mobile station and a wireline terminal, which is connected to the system via the local and/or long-distance networks. Referring to FIG. 1, whenever the mobile station 14 activates or roams into a MSC coverage area, i.e., the xe2x80x9ccellxe2x80x9d for which the MSC is responsible, the mobile station transmits the stored IMSI number to the serving MSC 10 via a base station (BS) 20. The IMSI number is transmitted over a radio channel 22 in a format complicate with TIA/EIA/IS-95 and detected by antenna 21 of BS 20.
Base station 20, in turn, transmits at least a portion of the IMSI number to the serving MSC 10, such as for example via communication line 24. The procedures and protocol for communication between the base station 20 and the MSC 10 have also been standardized. For an identification of industry standards relating to these communications, reference is made to TIA/EIA/IS634-A, xe2x80x9cMSC-BS Interface for Public Wireless Communication Systems.xe2x80x9d The format for messages between base station 20 and MSC 10 is a variable octet field.
In order to provide mobile service to the newly registered MS 14, the serving MSC 10 transmits a Mobile Application Part (MAP) based signal, such as a location update signal, to a home location register (HLR) 12 via a signaling link 26. Such a signal informs the HLR 12 of the network address associated with the MSC 10 currently serving the MS 14 and also requests requisite subscriber information for providing mobile service to the roaming MS 14. The HLR 12 updates its database to store the netwvork address representing the serving MSC 10 and also copies the requesting subscriber information to a visitor location register (VLR) 30 associated with the serving MSC 10. The net work address representing the serving MSC 10 stored in the HLR 12 is later utilized by the mobile network to reroute any incoming call intended for the mobile station 14 to the serving MSC 10. Accordingly, whenever a telecommunications subscriber dials a telephone number for the mobile station 14, the HLR 12 is queried by the mobile network to determine the current location of the MS 14. Utilizing the stored network address in HLR 12 representing the serving MSC 10, the HLR 12 requests a roaming number from the serving MSC 10 in response to the receipt of the query signal. The roaming number provided by the serving MSC 10 is then used by the telecommunications network to route the incoming signal towards the serving MSC 10. The serving MSC 10 then pages the mobile station 14 and accordingly establishes a speech connection with the mobile station 14, if available.
If MS 14 roams out of MSC 10 coverage area and into MSC 31 coverage area, MSC 10 will hand-off the communication to MSC 31 and base station 32. To ensure compatibility between two MSCs, the procedures and protocol for the format and transmission of messages have been standardized. For an identification of industry standards relating to these communications, reference is made to ANSI/TIA/EIA Standard 41, xe2x80x9cCellular Radio telecommunications Intersystem Operations.xe2x80x9d The format for messages between two MSCs, such as for example MSC 10 and MSC 31 for FIG. 1, as specified by ANSI/TIA/EIA-41 is an 8-octet structure as illustrated in FIG. 2, wherein each of locations A-H represents one bit in each of the eight rows. Additionally, some manufacturers utilize proprietary interfaces between an MSC and BS that utilize the ANSI/TIA/EIA-41 format.
There are some shortcomings, however, with conventional mobile systems used in the United States. Currently, only a portion of the information included in the IMSI number, specifically the IMSI_S parameter, is sent from the BS to the MSC. As such, information included in the MCC and IMSI_11_12 parameters is not utilized. A wireless communication system that utilizes only the IMSI_S parameter cannot support increased IMSI number functionality, since use of only the IMSI_S parameter allows the system to support only one IMSI class and type, i.e., a Class 0, Type 0 IMSI. Consequently, a CDMA telephone with an IMSI number that has a different class or type than Class 0, Type 0, will be unusable in the United States.
By complying with the requirements of ANSI/TIA/EIA-41, a wireless communication system can support increased IMSI number functionality, i.e., all types of IMSIs in both Class 0 and Class 1, by utilizing more of the information included in the IMSI number, such as for example the MCC and/or IMSI_11_12. However, since the IMSI number is received at the BS 20 from the MS 14 in a format that complies with TIA/EIA/IS-95, there exists an incompatibility from a network signaling standpoint since MSC 10 requires the IMSI number in a different format, i.e., a format that complies with ANSI/TIA/EIA-41. If the proper format is not used, a system will be unable to offer global roaming capability since only a portion of the IMSI number can be used, which will result in a loss of customers and corresponding sales. Therefore, it is necessary to convert the IMSI number received from the MS to a format compatible with ANSI/TIA/EIA-41.
Thus, there exists a need for a method and apparatus for converting an IMSI number in TIA/EIA/IS-95 format to an IMSI number in ANSI/TIA/EIA-41 format to support increased IMSI number functionality.
The present invention provides a unique method and apparatus for allowing a wireless communication system to offer increased IMSI number functionality and corresponding global roaming capability by converting an identification number received from a particular mobile station in the wireless communication system in a first format to a second format which allows for use of more information included in the identification number.
For example, a variable length IMSI number in TIA/EIA/IS-95 format is received at a base station in encoded form. The base station decodes the parameters included in the IMSI number into their original decimal values, and, if all parameters have not been sent in accordance with the IMSI type, will add the proper values for the unsent parameters. The MCC, IMSI_S, and IMSI_11_12 parameters of the IMSI number are then stored in a 15-digit IMSI array. The contents of each location of the 15-digit array are associated with a specific location in an 8-octet structure which is required by ANSI/TIA/EIA-41. The value in each location of the array is converted to Binary Coded Decimal (BCD) format and mapped to its associated location in the 8-octet structure. The IMSI number will then be in a format compliant with ANSI/TIA/EIA-41, thus allowing a service provider to offer increased IMSI functionality to its customers and allow the IMSI number to be used as a national mobile station identifier which will result in global roaming capability for CDMA telephones.
These and other advantages and features of the invention will become apparent from the following detailed description of the invention which is provided in connection with the accompanying drawings.